Two components are essential for a vaccine: an "antigen," which is typically a protein from a pathogenic microbe;and an adjuvant, which is a molecular signal to the immune system that the antigen is important and should be defended against. Typically, live attenuated viral vaccines for diseases such as influenza utilize the immunostimulatory nature of the virus itself to adjuvant the immune response. However, HIV virions typically do not induce dendritic cell activation following infection. In addition, the virus can actively suppress the immune response with accessory proteins such as Nef. Therefore, a challenge for live attenuated HIV vaccine development is to find an adjuvant capable of inducing strong immune stimulation that can also be encoded within the HIV genome. A potential source of adjuvant is the human immune system itself. Both the human body and viral pathogens are known to produce adjuvant molecules that can initiate and amplify human immune responses. These include CD40, GITR, OX40 and various genes that utilize the TRAF intracellular signaling pathway to activate immune cells. However, it was not previously known that these TRAF-mediated receptor molecules must be clustered. Such clustering can be artificially induced via a "multimeric" ligand where many trimeric ligand molecules are linked together. The main goal of this proposal is to identify TRAF-mediated intracellular signaling systems such as CD40L/CD40 that have the potential to induce dendritic cell immune activation. The project will then encode these genes within a single cycle SIV vaccine to enhance CD40 and other TRAF-mediated intracellular signaling pathways. The hypothesis is that this immunostimulatory single cycle SIV vaccine will result in increased dendritic cell licensing and maturation in vitro, and enhanced vaccine efficacy in animal models. PUBLIC HEALTH RELEVANCE: This project will develop new forms of immune-stimulating attenuated SIV that could significantly improve the strength of experimental AIDS vaccines. The result of these studies will establish whether attenuated HIV vaccines can be boosted using key components of the mammalian immune system or viral mimics of these molecules.